New, molecular heavy metal cluster immunoprobes will be prepared, with platinum and palladium clusters 1.8 and 2.4 nm in diameter covalently conjugated to antibodies to give immunoelectron microscopy probes. Multiple gold cluster complexes will also be combined in a single larger label, up to 5 nm in diameter, using starburst dendrimer molecules as carriers for undecagold and a larger 1.4 nm gold cluster complex. Syntheses are proposed for new dendrimers based on adamantylic initiator cores and chain branching monomers, and rigid rod spacers: these will be also be used as single-label carriers for multiple gold clusters. The resulting probes should combine the ease of visibility of larger colloidal gold particles with high sensitivity, low non-specific protein affinity, no aggregation or label dissociation, and penetration up to 30 micro into cells and tissue sections. New multiple gold cluster probes used with silver enhancement in antigen detection blots, should demonstrate unprecedented sensitivities, possibly an order of magnitude or more higher than current chemiluminescence methods. New dendrimers are proposed which incorporate gold clusters into the constituent monomers: these will be used as precisely defined immunoprobe labels up to 10 nm in diameter, and will also be studied as potential precursors to new classes of materials.